dummie detected

Welcome. FTR, not having MP3 codecs installed by default has nothing to do with Ubuntu. They are third-party and you need to agree to install them personally. Ubuntu can't do anything about that. Nothing silly about it.

They are easy to install. You can tick the box that says 'Install third-party drivers' when installing or install ubuntu-restricted-extras when installed and reboot.

As for installing the Steam client, you might be better supported if you post a new thread about that in Gaming and Leisure perhaps. I know nothing about it but will say this: Software Centre (or Ubuntu Software or Gnome Software or Synaptic Package Manager, whichever package manager you are using) is your friend. Have you looked in there for Steam stuff?